Topic: Texas Barn Find - 1974 CB750K4 - HELP ME OUT!!!

[oldhatt45]

Funkenstein,

Forgot to mention another tool that will pay for itself. 
When rebuilding the Master Cylinder (Front Brake) there is a C-Clip in the barrel of the Master Cylinder.
That 1 C-Clip has given more people a headache when trying to remove it.
A suggestion would be to spare yourself the aggravation and get the right C-Clip removal tool.
http://www.motionpro.com/motorcycle/partno/08-0279/

Your list looks Good for starters.  Just take your time and do it right. 

If you use soap and water to clean your tank out, and it gets some or all of the Gunk out, give it a little Marvel Mystery Oil, or WD40 or something to protect the metal from re-rusting (aka Flash Rust).  Would probably guess that you will need something stronger, but, as long as you're not in a rush, go for it.  Can't hurt. 

Charlie

[calj737]

Yes, soap and water inside the tank to remove the dirt and grime. Then deal with the rust.

Your list of To-Dos is a bit excessive. Mainly, I'd leave the engine sealed if it frees up, rotates cleanly, and ultimately fires. To deal with a rebuild/tear down, the motor must come out of the frame. Not a big deal, by why do it on a motor with 900 miles?

Disassembly of the swing arm and cleaning and regreasing is a very good idea. Deal with any rust everywhere. And check out the bottom of Wilbur's signature for a comprehensive thread on refurbishing your wiring harness and connectors. This will pay huge dividends.

And like all your cables really well 

[SOHC4 Cafe Racer Fan]

You should also add new bearings:
(1) Replace balls in headstock with tapered roller bearings (All Balls)
(2) New wheel bearings
(3) New bronze swingarm bushings

Personally, I'd ditch the points and go with electronic ignition, too.

[edwardmorris]

.............. I'd leave the engine sealed if it frees up, rotates cleanly, and ultimately fires. To deal with a rebuild/tear down, the motor must come out of the frame. Not a big deal, by why do it on a motor with 900 miles?......

+1

I see your to-do has a bunch of stuff to replace, if you're going to stick with OEM parts as recommended, PM me for JT's email. jtmarks77 is his ebay seller id, and he is THE go to guy for OEM/NOS/Yamiya stuff without having to deal with ebay fee/shipping and customs from JP in case of yamiya items etc. as he can invoice you directly for parts you're purchasing.

[Stev-o]

These guys are just creating ways to waste your time and spend your money.

If I were you, I'd sell it to Stev-o for $1000 more than you paid, then you can go down to 6th St and party with the college girls!

[turboboxer6spd]

So do the pictures work for anyone else? Using Tapatalk here

[Funkenstein]

Funkenstein,

Forgot to mention another tool that will pay for itself. 
When rebuilding the Master Cylinder (Front Brake) there is a C-Clip in the barrel of the Master Cylinder.
That 1 C-Clip has given more people a headache when trying to remove it.
A suggestion would be to spare yourself the aggravation and get the right C-Clip removal tool.
http://www.motionpro.com/motorcycle/partno/08-0279/

Your list looks Good for starters.  Just take your time and do it right. 

If you use soap and water to clean your tank out, and it gets some or all of the Gunk out, give it a little Marvel Mystery Oil, or WD40 or something to protect the metal from re-rusting (aka Flash Rust).  Would probably guess that you will need something stronger, but, as long as you're not in a rush, go for it.  Can't hurt. 

Charlie

I was wondering about "flash rust" but I've never heard that term before. Picking up some MMO, Acetone and Metal Rescue tomorrow. Thanks for the heads up! As for the tool, I'll order one first thing tomorrow also. Thanks again!!

Your list of To-Dos is a bit excessive. Mainly, I'd leave the engine sealed if it frees up, rotates cleanly, and ultimately fires. To deal with a rebuild/tear down, the motor must come out of the frame. Not a big deal, by why do it on a motor with 900 miles?

Disassembly of the swing arm and cleaning and regreasing is a very good idea. Deal with any rust everywhere. And check out the bottom of Wilbur's signature for a comprehensive thread on refurbishing your wiring harness and connectors. This will pay huge dividends.

And like all your cables really well 

Thanks calj737! I do want to keep this limited to just getting her up and running so I've shortened my list to a best case scenario. At the same time I want to make as many safety improvements as possible especially in regards to the brakes, suspension and steering. Check out the new list below!

You should also add new bearings:
(1) Replace balls in headstock with tapered roller bearings (All Balls)
(2) New wheel bearings
(3) New bronze swingarm bushings

Personally, I'd ditch the points and go with electronic ignition, too.

Thanks, I added those items to the future list. I'm so tempted to add the ignition to the list. I need to do my research but I really appreciate your input! I never owned a vehicle with carbs or points before so this is all new to me. I want to stay stock so I guess that means the points and all their problems.

Revised List:

Done:

• Buy lottery ticket!
• Buy hondaman's book!
• Buy JIS tool set.

Saturday:

• Remove side covers being very careful. Lube and press from the inside. Go slow!
• Remove gas tank. Clean with soap and water. Inspect and possibly use metal rescue. Electrolysis if still major rust present.
• Remove petcock, rebuild, repack
• Drain oil from oil tank. Drain oil from pan(if more than half a quart, oil stopper in the oil pump has leaked, needs rebuilt)
• Remove spark plugs and add 50/50 mix of ATF and Acetone to fill cylinders. Let it sit for a week.

Future:

• Rebuild front brakes, new pads, replace fluid, new SS brake lines(use heat to free master cylinder and caliper
• Rebuild Master Cylinder - Very likely the brake fluid had turned to Goooo.  (Use only DOT3 fluid)
• Rebuild Caliper - New O-Ring seal, New Stainless or Phenolic piston.
• Rebuild front suspension, fork seals, fork oil, progressive springs
• Refurbish swing arm with new grease. New bronze swingarm bushings
• Replace balls in headstock with tapered roller bearings (All Balls)
• New Sprockets and Chain.  Not from wear, but from age.  Sprockets are probably OK but the chain has probably rusted.
• Remove carburetors, rebuild(harisuluv)
• Replace spark plugs with D8EA plugs
• Check the electrical connectors for oxidation. Inspect/Repair Electrical System
• Inspect/Rebuild rear brakes.
• Rebuild/Upgrade rear suspension.
• New Tires. New wheel bearings.

I was able to take a picture inside the oil tank on the right side of the bike.

[SOHC4 Cafe Racer Fan]

You should also add new bearings:
(1) Replace balls in headstock with tapered roller bearings (All Balls)
(2) New wheel bearings
(3) New bronze swingarm bushings

FYI - these are all cheap things to do that yield rewards in safety and handling.  They can help prevent a death wobble.

[2strokeTrush]

Keep your points but buy a Hondaman System as well

[DennyK]

Great find. down in Texas.  I found a K4 in Colorado with 13000 miles that was parked in a garage for 8 years; the front brake was locked on the disk but the engine did turn over with the kick starter.  The bike had been stored on the kick stand, so the one side of the carbs was pretty clean but the other was a mess, ultimately got the carbs cleaned using ultrasonic and that worked very well.  When you rebuild your carbs, be aware that your floats may not be good, i.e. they have small holes and do not float.  Regarding the front brake, save yourself some grief and buy a new master cylinder.  I used the grease gun method to get the old brake pad out.  Once your engine frees up and you can get fuel flowing into the carbs you can then determine how it rides.  Likely you will want to replace the fork springs and shocks as well as the work you are doing on the swing arm.  At this point I am in the middle of a top end and rebuilding the bike from the ground up.   Good Luck with your project...I'll be watching.

[Trad]

Super cool find! I look forward to seeing it come back to life. You really have an easy starting point compared to most. Lucky guy.

[calj737]

I'm wondering if the "stuck engine" isn't more to do with stuck clutch plates, than stuck piston rings. Remind, does it roll and shift into neutral? I seem to recall you saying it had soft pressure from the levers.

Still certainly possible for the piston to be stuck, but I do find it curious that it would be so. There's little evidence of rust on the bike, it was "sealed" with an exhaust and stock induction system, and generally it's pretty arid where you are, isn't it?

I suppose it's possible, but it surely does surprise me. And be mighty, mighty, careful with the Acetone near your paint. It will eat paint almost as fast as DOT 3 Brake fluid.

[oldhatt45]

Funkenstein,

Your Oil Tank Looks Fine!  I would not touch it any further.
How much Oil came out of it??  This could be an indication of Oil Pump condition.

If you haven't done so already, read my build thread.  (Click on the link below on my signature line.)  I have done about everything you are looking at doing as far as Brakes, Swingarm, forks, shocks, Gas Tank, Clutch, etc.  goes.  It will at least give you some info that you can then ask questions about.

Go Slow.  The guys here will help you with whatever info you need.

Charlie

[Funkenstein]

Keep your points but buy a Hondaman System as well

Agreed! Added to list. Thanks!!

[Funkenstein]

I'm wondering if the "stuck engine" isn't more to do with stuck clutch plates, than stuck piston rings. Remind, does it roll and shift into neutral? I seem to recall you saying it had soft pressure from the levers.

Still certainly possible for the piston to be stuck, but I do find it curious that it would be so. There's little evidence of rust on the bike, it was "sealed" with an exhaust and stock induction system, and generally it's pretty arid where you are, isn't it?

I suppose it's possible, but it surely does surprise me. And be mighty, mighty, careful with the Acetone near your paint. It will eat paint almost as fast as DOT 3 Brake fluid.

I tried shifting the bike last night. I have a neutral on the bottom and can shift up 2 gears. It hits a hard bottom and a hard top otherwise it feels like a normal shift. Weird thing was... I could shift the gears even if I wasn't hold the clutch handle. The clutch handle feels like it engages something and returns to it's home position easily. Any ideas about that? I don't want to shift it too much until I get more info and oil onboard! haha!

I am really worried about the acetone actually. The tank and side covers will be well far away when I'm messing with that stuff. But is MMO just as toxic to paint? Maybe I should use MMO instead of the 50/50mix?

The barn is in the Texas plains area. Moderate rainfall at best. Drought-like sometimes too. This bike has it's share of rust. I think I'll keep most of it for now unless it's a safety or degradation issue. I mean, if I keep it dry, the rust won't get much worse very quickly right?

[Funkenstein]

Funkenstein,

Your Oil Tank Looks Fine!  I would not touch it any further.
How much Oil came out of it??  This could be an indication of Oil Pump condition.

If you haven't done so already, read my build thread.  (Click on the link below on my signature line.)  I have done about everything you are looking at doing as far as Brakes, Swingarm, forks, shocks, Gas Tank, Clutch, etc.  goes.  It will at least give you some info that you can then ask questions about.

Go Slow.  The guys here will help you with whatever info you need.

Charlie

Hey Charlie! I haven't touched anything yet so that's the oil level she came with. Have no idea what that means as far as oil pump condition. I've been checking out your build thread already and it looks like we're treading the same territory. You really went all out to get the rust out! haha! I'll be hitting you up for sure! Thanks for your help!

[70CB750]

You have to understand the 750 is a dry sump bike.  Means the oil is kept in the oil tank, not in the oil pan.  There is a part of the oil pump, that prevents the oil leaking into the oil pan when the engine is not running.   Over the time, this valve deteriorates and the level in the oil tank would be low, while the bike is full of oil.  It leads to beginner's mistake of topping the oil tank and overfilling on oil.

That said, the best time to check oil level is right after you shut the engine down.

Also, here is a schema of the oil circulation, it helped me a lot to understand how the oil is moving around.

[754]

I doubt the neck, wheel or swingarm bearings had a chance to wear out..not in the 40 hours. Or less that is on the bike.
 When putting the oil mix in the cylinders, don't put too much in, or it wont he able to turn, if it dies get unstuck.

[754]

The oil pump seal is not necessarily. Bad.. It sat for a long time, the oil always run into the engine..
Often in as little as a few months or a year.

[calj737]

MMO is not toxic to paint, and since you'll have the painted parts well away from the bike, go ahead with the mixture to unstick the pistons. Don't worry about overfilling them, as long as the plugs are out when you attempt to rotate the crank, theres no issue of hydro-locking the motor.

Not being able to shif above 2/3 without running the engine is normal. Sounds like your clutch may not be "engaging" meaning the plates are returning to a friction position since you can shift easily without the level actuated. All pretty normal conditions of a "sat awhile" bike 

Im not a "stock, restored" type of guy, but this project holds unusual appeal to me for some reason. Its like finding a time capsule I guess... The unusually low miles is probably the magnet for me.

[oldhatt45]

Funkenstein,

The diagram that 70CB750 put up in replay #66 is something you should definitely study!
It provides a lot of information on the Oil Flow through the engine.  Understanding that will help you understand what's going on.

While there is a chance that there is nothing really wrong with the seals in your  oil pump (with only a few miles on her for wear), proper lubricating of the 750 engine is a must.  A bike that has been sitting for as long as yours (and mine ) is subject to just plain age  deterioration of some of the rubber parts and certain springs.  Given that the Oil Pump is vital to engine operation, my personal opinion is that it should be in known GOOD condition.  For the price of Elan's Oil Pump Super Kit, I would plan on rebuilding it.  It's cheap insurance. 

Also, since the picture you posted shows almost no oil in the Oil Tank, I would almost guarantee that when you pull the drain plug, there will be 2 to 3 quarts of oil coming out.  So just be aware of that. 

Charlie

[Funkenstein]

Saddle Bags and Fairing mounts/brackets

I thought I'd post some pics of the brackets and mounts for the saddlebags and fairing. I've seen people online looking for mounts for their saddle bags so I thought I'd get some detail pics for reference. It seems to be some kind of kit as it's stamped:

HONDA CB
750 SBB






The bottom bracket for the fairing is below the headlight mounted a side screw to the triple tree.

[Funkenstein]

Funkenstein, what is good in life?
To wrench with your buddies who have driven before you and hear lamentations about their women.
haha!
I had some friends over on Saturday and we cracked some beers, turned some wrenches and started pulling the bike apart. I took a bunch of pics and have a bunch of questions so let's get started!

First off, I removed the old saddle bag brackets and mounts for the fairing. I decided to leave the engine guard/highway bars on for now for protection in case the bike falls over while I'm working on it. Next, I removed the seat and stored it away with it's hardware. That left me looking at this:



So I decided to pull the battery next. Is that paper inside it??


That manufacture date says JULY 1973. Fits in with the 9/73 manufacture date of the bike listed on the front fork sticker. Also, Yamaha distribution?


On to the tank! I cut the fuel lines, they were cracked anyway, and pulled the tank loose from the frame. Guess what? More mud daubers!! The bike's nickname is definitely "The Mud Dauber" from here on out. The tank looks super clean with only a couple spots of surface rust on the bottom.




The first evidence I have that someone has messed with the bike comes from the petcock bowl. Someone bent up the nut and put some tool marks on the sides. It came off pretty easily for me.





The tank still had about half a gallon of 40 year old gas in it. I emptied it out and got busy with the Dawn soap and water.



4 tankfuls later...



Now we go inside the tank!!!




I think this shot shows off what I'm dealing the best. It doesn't look like rust. Can you see the bare metal at the bottom of the tank? I think it's all just gunk and varnish. What is everyone's opinion about getting rid of that? I don't want to harm the pain on the tank so was thinking of MMO and letting it sit; rotating every few days.



So I was ready to do the 50/50 mix of Acetone and ATF into the pistons via the spark plug holes. Man these plugs look good for being 40 years old!!



After removing the spark plugs, I ran into another issue. I can't see down into the 2 and 3 pistons so I decide to take a picture with my phone. Bollocks!!



That's another damn mud daubers nest and I guarantee I knocked a little of that into the cylinder!! I put all the spark plugs back into the bike and wheeled it out onto the driveway for another bath. The picture below is not cat poo, it's part of the more than 10 pounds of mud deposited all over this bike by these crafty insects.



While it's out and getting washed, I decide to take off the side covers. Holy crap, they're plastic?!? I didn't even tap on them before this. All the advice of going slow and pushing from the inside paid off; No Broken Tabs!!!!




On the other side, more mud daubers!!!



I cleaned for 2 hours and went through 3 used toothbrushes hitting every nook and cranny. Then I did a light spray of WD40 on some of the rusty spots. I also popped off the tub on one of the carburetors. Ugly!!! I still have to decide if I'm going to tackle this part of the project myself or send it off.



Tonight I'm draining the oil and putting the 50/50 mix in the spark plug holes. I'll post some more pics and questions after that. Thanks for stopping by!!

[oldhatt45]

Funkenstein,

That gas tank looks like it will need more than Dawn & Water.
I did a 1 week Cleaning Vinegar soak to start with on mine.
Then I did a 1 hour deal with the Prep & Etch and my tank is now fine and ready to be used.

Those Mud Daubers are definitely a PITA.  Glad I didn't have to deal with them.   

But you're doing it right.  Go slow.  One thing at a time. 

Charlie

[Stev-o]

+1  Try soaking the tank with white vinegar, get it at HEB.

The carb float bowls do not look that bad, luckily you dont have white corrosion in there. Best way to clean carbs is with an ultrasonic cleaner.